Practical Characteristics of LEDs

The first thing to know about light emitting diodes (LEDs), and all diodes, is that they are current devices, not voltage devices. Power supplies for LEDs are typically designed to drive them with a constant current. For easy estimates, the forward voltage of a diode is a constant. Forward voltage depends on the temperature of the die, and this depends on how big the package is. The same diode in a bigger package will stay cooler, and thus have a higher forward voltage. Rectifier diodes and LEDs fall into the unintentional category. If they conduct in the reverse direction, there is an excellent chance that they have broken. Now with rectifier diodes, there is an easy solution. This chapter talks about quite a number of parameters for LEDs, as well as their temperature variations. Realizing how much the variation in some of these parameters influences performance, manufacturers offer binning.